1. Field of the Invention
The present invention relates to a multimedia search. More particularly, the present invention relates to a method for performing a multimedia search using a histogram such as a color histogram as a multimedia feature for the search.
2. Description of the Related Art
Recently, various techniques for a content-based multimedia search have been introduced. In those techniques, a histogram such as a color histogram is generally used for the search. The histogram represents feature distribution of the multimedia, and especially, the color histogram is considered as the most important feature information among various histograms used for the search.
The color histogram is the information that represents color distribution of the multimedia data such as an image, and the number of bins for the histogram is determined based upon how a color space is quantized.
Generally, the respective bin values are expressed by fractions. However, for a higher performance and spatial efficiency, the bin values can be expressed by N bits whose space is smaller than a fraction-expressed space. For instance, it is generally known that the space can be saved without deteriorating any substantial performance if fractional values in the range of 0 to 1 are expressed by 8-bit, i.e., 256 numerical values. As explained above, the quantization of the color space and the quantization of the histogram bin value should be considered in describing the color histogram.
The method of quantizing the bin value or the color space can be classified into a uniform quantization and a non-uniform quantization.
The uniform quantization means a uniform division of the bin value or the color space based on a reference axis of quantization, while the non-uniform quantization means a non-uniform division of the bin value or the color space.
For example, in case of the bin value quantization, the method of uniform quantization divides the values in the range of 0 to 1 by a uniform width to uniformly quantize the values, while the method of non-uniform quantization divides the values by a non-uniform width to non-uniformly quantize the values.
The non-uniform quantization method can achieve a higher search performance than the uniform quantization method or the method of describing fractional values as they are. For example, the search performance can be increased if a section having relatively important bin values is closely divided and a section having non-distinctive bin values is sparsely divided in describing the multimedia feature.
For example, in case of the histogram, most of the bin values are smaller than 0.2. So, it is meaningless to closely divide the bin values larger than 0.2.
Also, in case of the color space quantization, there exist portions where color points that constitute the multimedia data are concentrated or sparse in the whole color space, and the search performance can be increased by more closely dividing the concentrated portion.
The non-uniform quantization method has a relative advantage as explained above. However, the non-uniform quantization method has a problem that it should be applied as a different format for respective applications.
First, let's consider the color space quantization. In case of a general photograph, most of colors are concentrated in a region that purity is low. So, it is advantageous for the search to divide the region of the low purity. However, in case of the multimedia such as an animation, the colors are concentrated in a region of high purity. Also, in case of a black and white image such as a medical image, only black and white region in the whole color space is used for search, and thus it is not required to divide most of other color regions.
Also, in case of the bin value quantization, most of bin values are distributed in a region that the bin values are smaller than 0.2. However, in an exceptional case such as the medical image, the colors are concentrated in the black and white region, and thus bins having values larger than those of other multimedia may be produced.
As described above, in order to obtain the optimum performance, different type of color space quantization or bin value quantization should be applied for respective applications.
However, if different quantization method is applied for respective applications, a compatibility problem occurs. In other words, it is impossible to identify and search data quantized by the different quantization methods.
Meanwhile, standardization activities have been progressed to enables multimedia data search, irrespective of the kinds of data providing servers. For the purpose of the standardization, however, it is very difficult to use the non-uniform quantization method. Accordingly, it is required to provide a desired search method having high-performance, satisfying an interoperability that the standardization aims as well as providing the optimum feature information for respective applications.